Froth flotation apparatus and process



Aug. 13, 1935. MS. HANSEN FROTH FLOTATION APPARATUS AND PROCESS Filed Oct. 5, 1952 4 Sheets-Sheet 1 z A TTORNEYJ Aug. 13, 1935. M. s. HANSEN FROTH FLOTA'IION APPARATUS AND PROCESS Filed Oct. 5, 1932 4 Sheets-Sheet 2 INVENTOR.

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Aug. 13, 1935. M. s. HANSEN FROTH FLOTATION APPARATUS AND PROCESS Filed Oct. 5, 1932 4 Sheets-Sheet 3 I N VEN TOR.

A TTORNEXi Aug. 13, 1935. M. ,s. HANSEN FROTH FLOTATION APPARATUS AND PROCESS Filed Oct. 5, 1952 4 Sheets-Sheet 4 I N VEN TOR. I

A TTORNE Y.

Patented an 13, 1935 UNITED STATES PATENT OFFICE morn FLOTATION APPARATUS AND PRO ES mm... s. Hansen, Speedway City, Indianapolis, 11:31., asslgnor to Peter C. Reilly, Indianapolis,

Application mm 5, 1932, semi No. 030,310

4' Claims. (01. 250-107) This invention relates to improvements in ap- *paratus used in the well known agitation-froth flotation process and also to improvements in that bles separate, in the aggregate, as a froth which 1 is easily removed from the circuit for recovery of the mineral it carries. It is further recogmzed that the efiiciency with which this agitation and induction of air into the circuit is accomplished constitutes one of the major factors in determining the economy 'of the operation.

- The agitation-froth flotation cells of the type heretofore used have consisted essentially of two chambers; one, the agitation chamber, in which the impeller operates, for the agitation and aeration of the flotation circuit; the other, the froth settling chamber, for the separation and collection of the mineral-laden froth. These chambers are separated by a vertical wall provided with two vertically spaced, comparatively small openings. An impeller or other agitating means located in I the agitation chamber serves to agitate the pulp thereby incorporating air and producing a froth; and, at the same time, to induce circulation of the fluid pulp upwardly through the agitation chamber, outwardly through the upper one of the two openings just mentioned into the settling chamber, downwardly through the settling chamher, and thence through the lower opening into the agitation chamber. There is also a minor pulp circuit, in'which the pulp flows downwardly 1 along the walls of the agitating chamber instead of through the separating chamber.

In these prior flotation cells, the agitating and separating chambers had a common vertical plane of symmetry. Both dimensions of the agitating chamber in horizontal cross-section were More specifically this invention deals,

wealth not otherwise-available. So far as I am aware, no significant changes in basic design and/or orientation of parts which have contributed in any material way to the emciency and economy of operation havebeen suggested or applied prior to the invention of this application.

It is the object of my invention to produce an improved agitation-froth flotation unit and an improved cell and impeller arrangement, and thereby to increase the recovery of mineral obtained, to decrease the cost of the flotation operation, and to render the results obtained with the unit more uniform and dependable and less subject to variations arising from the human factor. More specifically, it is my object to produce a unit in which the agitating and separating chambers are arranged to facilitate the separation of mineral-laden bubbles from the remainder of the pulp and to so shape the agitating chamber, and to so locate the impeller therein, that the incorporation of air in the pulp and the formation ofbubbles are speeded and increased. .Another object of my invention is to provide an improved form of agitating impeller which will be more effective for its intended purpose, especially when used with my improved cell arrangement, than are impellers ofthe type used in the past.

In carrying out my invention, I so shape the agitation chamber and so locate the impeller therein as to interrupt the symmetry of the vortex produced, and desirably to produce secondary swirls and vortices i n;the liquid and thus increase the agitating effect of the impeller and the resulting induction of air bubbles into the pulp. Further, in my improved cell I space the impeller a considerable distance from the wall between the agitating and the settling chamber, and provide relatively free communication between such two chambers, conveniently by the use of ,a single opening of considerable vertical extent; and thereby get more ready circulation without interfering with the separation of the mineral-laden froth from the liquid in the settling chamber.

The accompanying drawings illustrate my invention: Figs. 1 and 2 are side and front views, respectively, of a laboratory agitation-froth flotation unit including a cell and impeller embodying my invention, the cell in Fig. 1 being shown in vertical ores-section taken on the line ll of Fig. 2; Fig. 3 is a plan of the cell shown in Figs. 1 and 2; Fig. 4 is a view similar to Fig. 3, but showing an impeller in place in the, agitating chamber and also illustrating the vortical action induced by operationof the impeller; Figs. 5 and 12 to are isometric views of modified conven-.

tional cells showing arrangements by which my invention may be embodied therein.

In the complete assembly shown in Figs. 1 and 2 there is a stand l which supports a variablespeed electric motor I to the armature shaft of which there is secured the shank 4 of a suitable impeller. as by means of a chuck I. The stand I also supports a rheostat 6 having a control lever i by which the speed of the motor may be controlled. A flotation cell 1a, to be described in detail hereinafter. is mounted below the motor 2 conveniently through the medium of slotted feet which receive headed pins I projecting outwardly from the face of the rheostat O.

The cell Ia comprises an agitating chamber II and a settling chamber ii. The agitating cham-' ber i0 is of oblong contour in horizontal section. as is clear from Figs. 3 and 4, and the settling chamber Ii is located near one end of one of the longer sides of the agitation chamber and proieots outwardly therefrom. A bridge wall I! with its lower edge at about the normal liquid level separates the settling and agitating chambers,

and below the wall the two chambers are in corn-v munication with each other through an opening I which extends downwardly to the bottom of the chambers. The settling chamber H has the usual side walls It and an outwardly and upwardly sloping bottom it terminating in a lip it over which mineral-laden froth discharges.

The impeller shown in Figs. 4 to 6 is of the conventional type and embodies a vertical shaft 22 to which there are affixed an upper set of inclined blades fl and a lower set of similarly inclined blades 24. This impeller is located near the opposite end of the agitating chamber from the opening it. This non-central location of theimpelleris an important factor of my invention, as will more fully appear hereinafter. Y

Figs. 8. 9, and 10 illustrate diiferent forms of cells embodying the same general arrangement of agitating and separating chambers and impeller shown in Figs. 4, 5, and 6. In Fig. 8, the agitating chamber it is of greater length than that shown in Figs. 4, 5, and 6. the opening I4 is located near the center of one of its side walls, and two impellers are used, one. near each end of the agitating chamber. agitating chamber associated with two separating chambers located on opposite sides of and parallelto the agitating chamber, the impeller being located in one end of the agitating chamber and the two openings H, which afford communication respectively with the two settling chambers. being located near the other end. In Fig. 10, the agitating and separating chambers areshown as co-planar. the opening it being located in one end wall of the agitating chamber. Fig. ll illustrates the type of agitation-froth flotation cell of Figs. 3 to 7, and shows a method of charging and discharging the circuit from the agitation chamber ill by means of pipe lines 27,

'28, 29, 80, and Si when the cell is used in commercial practice. The pipe lines 21 and 28 may be used as the inlet and outlet of the circuit respectively, while the pipe lines 29, 30, and ii, and valve 32, may be used for circulation of the circuit. when this is done, the valve 32 is closed and the pipe 3| connected in any suitable pulp- Fig. 9 shows a single,

circulating circuit whereby the desired circulation is induced in the agitation chamber It. Likewise the pipe lines 28. 30, and SI, and valve I! may be used for charging and discharging the circuit from the agitation chamber or they may be used to supply additional air, gases or other liquids to the flotation circuit.

In all the cell-forms so far described, it will be noted that the shape of the agitating chamber is not symmetrical with respect to any axis of symmetry, that the impeller is located in an eccentric position spaced from the opening into the settling chamber, and that such opening is of considerable vertical extent to provide free communication of liquid between-the two chambers. The specific rectangular cross-sectional shape of the cells shown is not essential. for other elongated or oblong cross section shapes are suitable'. Throughout this specification, I use the word oblong in a general sense, to mean any by modification of such conventional cell to disturb the symmetry of the vortex produced by the impeller. Some such modifications are shown in Figs. 12 to 15.-

In all of Figs. 12 to 15, I have shown a flotation cell of the conventional type, with an agitation chamber In square in cross section and a settling chamber H with the usual side walls I! and an outwardly and upwardly sloping bottom II. The wall between the agitating chamber ill and the settling chamber ii terminates short of the bottom of the. cell to provide a lower opening I0 providing communication between the two chambers. The upper opening II is also provided in this wall at about the normal liquid level, and this opening is provided with an over-hanging lip 52 on the side of the wall toward the settling chamber.

As heretofore used, this conventional cell has, been operated with the impeller located substantiallyon the axis of symmetry of the agitation chamber.

In Fig. 12, I have shown a cell andv impeller arrangement modified from this standard practice so that the vertical shaft of the impeller is located near one corner of the agitation chamber -ll rather than at the center of such agitation chamber. The particular corner near which the impeller is located is of less importance than the eccentric location of the impeller, but I have found that good results are obtained with the impeller located near one of the corners formed between the wall separating the two chambers and the side walls.

Another modification involving a change of position of the impeller is shown in Fig. 18. Here, the impeller shaft is disposed diagonally in the agitation chamber it, so that its axis approaches coincidence with a line connecting one lower corner of the agitation chamber and an oppo'si upper corner.

In both the modifications shown in Figs. 12 and 13 the swirl produced in the circuit by the impeller will be unsymmetrical with respect to the axis of the impeller, by reason of the unsymmetrical position of the chamber walls with respect to the impeller. with the symmetry of the vortex thus disturbed, the beating effect of the impeller will be greatly increased and a larger number of air bubbles will be entrained in the circuit.

In Fig. 14. I have shown a cell in which this disturbing of the symmetry of the vertex is prolylocated with respect to the impeller 22.

old cross-bladed type of. impeller is used here for duced by a vertical baffle 54 projecting from one wall of the agitation chamber l0, here shown as the back wall.

In Fig. 15, I have shown a cell particularly adapted for use in a flotation operation where several cells are connected in series by pipes so that the pulp is conveyed successively through the different cells, each cell taking out part of the mineral contained in'such pulp. In previous arrangements of this sort, care has been taken to introduce the pulp into any particular cell in.

such a way that it will not disturb the normal symmetry of agitation in that cell. In contrast to this, I introduce the pulp into a particular cell through a pipe 56 which discharges approximates 1y tangentially into the swirl produced by the impeller but in a direction opposite to the direction of travel of the pulp at that point in the swirl, and I discharge this incoming pulp with considerable velocity; so that the incoming pulp and the swirling pulp impact and the ncrmai symmetrical vortex produced by the impeller is destroyed. The out-flowing pulp is desirably withdrawn, as through a pipe 51, at a point near the bottom of the settling chamber.

In order to make clear the vortical agitating action in a flotation cell arrangement embodying my invention, especially in a cell of oblong crosssection, I have shownin Figs. 4, 5, and 6 the path of movement in the circuit. Owing to the oblong contour of the agitating chamber and to the eccentric location of the impeller, there are produced a plurality of vortices 34, 35, and 35. The

vortex 34 is rather closely concentric with the impellpr, while the vortices 35 and 38 are eccentrical- The illustrative purposes because of the lexer degree of agitation it produces and also because of the clearer cut definition of the fundamental effect in the circuit.

The shearing action of the blades occurs at the circular paths traversed by the edges'of the blades as the impeller rotates, and, as the vortices 35 and 36 (and also, but to a much lesser extent, the vortex 34) are eccentric to the axis of the impeller, the impeller blades may therefore be regarded as shearing the pulp on curved paths which are eccentric to a vortex-axis. The impeller shown in Figs. 1 and 2 embodies a plurality of downwardly and outwardly inclined pulp shearing rods and belongs generically to the type of impeller more fully described in my co-pending application Serial No. 680,635, filed July 15, 1933. When such an impeller is used in the process of this application the curved paths along which shearing of the pulp occurs near the bottom of the cell are of greater radius than those near the top of the cell. This results in deepening the vortex and increasing its surface, thus increasing the rate at which air is entrapped in the pulp.

With the impeller located at the opposite end or the agitation chamber from the opening into the settling chamber, any turbulence communicated to the settling chamber through the relatively large opening consists mainly of small eddy currents, and is in no way excessive or detrimental to the separation of the froth.

By contrast, in the conventional type of agitation-froth flotation cell with its impeller centrally located, only a single vortex is formed within rotation of the impeller shaft. The effect of the impeller is largely to circulate the pulp through the two chambers by way of openings that are necessarily restricted to prevent excessive turbulence in the settling chamber.

My agitation-froth flotation apparatus may be made from any suitable materials; for example, wood, glass, brick, concrete, metals and alloys. However, for laboratory use it is preferable to construct the apparatus, and particularly the impeller and flotation cell,-of metal such as cast iron or steel, and provided with a surface covering of smooth vitreous enamelon all faces which may come in contact with the flotation circuit; or the entire cell, inside and outside, may be thus coated with vitreous enamel. This prevents the flotation circuit from becoming contaminated and aifected by the material of the flotation apparatus, and likewise this same desirable result may tional type cell having its impeller located near one corneras illustrated in Fig. 15-, (3) with a conventional cell modified by the addition of a battle, as shown in Fig. 14, and (4) witha new type cell, shaped as shown in Figs. 3 to 6.

The conditions under which these flotation operations were run were kept as nearly constant as possible except as to the amount of frother used. In each case, 50 grams of pure mineral chalcocite was placed in the cell together with 50 cc. of water and 15 cc. of saturated lime water. This mixture was agitated with the impeller for one minute, when the motor was stopped, and the frother, as a water solution (0.5 mg. terpineol per cc. of water), and the collector (dibutyl dithiophosphoric acid in the proportions of 0.07 lb. per ton of mineral) were added, and the mixture was again agitated for one-half minute. Water was then quickly added to bring the liquid up to the level of the, lip; and the froth taken for an interval of one minute, and then for an interval of six minutes. The hydrogen ion concentration of the circuit was pH 9.1. The speed of the impeller was maintained constant at 2400 R. P. M. The amount 01 frother used was varied between the proportions of 0.02 pound per ton of material and 0.20 pound per ton of material, as shown in the following table.

This following table tabulates the total recovcries in percentage of chalcocite (Cues) The examinationof the foregoing table shows clearly the increase in recovery obtained by modifying the cell and impeller arrangement in accordance with my invention. It is to be noted that while in the conventional type cell with the impeller located centrally the optimum recovery of 90% ,was obtained with 0.16 lb. of frother per ,5 ton of mineral, a substantially equivalent optimum recovery was obtained in a similar cell with the impeller in eccentric position by the use of only about 0.12 lb. of frother per ton of mineral, and with my new oblong cell having its impeller at the end opposite from the opening into the separation chamber, an optimum recovery of 92% was obtained with only 0.085 lb. of frothcr per ton of mineral.

Further, the three arrangements which embodied my invention showed a much more rapid recovery than the conventional arrangement, and this was especially pronounced in thecase of the oblong cell. For example, in the run with 0.12 lb. of frother per ton of mineral, the flrst minute interval, during which froth was taken from the conventional cell, yielded a recovery of 11.4%, and the subsequent six minute period a recovery of 47.0% while on the similar run with my oblong cell, the flrst minute interval yielded 76% recovery and the subsequent six minute interval 20.0% recovery. Further, with 0.20 lb. per frother per ton of mineral, the change of the impeller from a central position to the eccentric position in the conventional cell changed the ratio of recovery between the two periods from 34% for the one minute interval and for the six minute interval to 80% for the one minute interval and 9.2% for the 6 minute interval.

While in this specification and in the drawings, 7

I have discussed and shown apparatus primarily intended for laboratory purposes, it will be obvious that the same principles will be applicable to flotation cells of a commercial size, for these commercialcells differ from the laboratory cells mainly in their size. The principles of operation are substantially the same.

In addition, while the foregoing examples of flotation operations carried out with apparatus involving my invention are limited to the recovery of a single mineral, the particular operations described were given only by way of example; and the principles embodied are applicable to the recovery of other minerals, including both oxidized and non-metallic minerals, as well as to the recovery of many substances which are not minerals at all, such for instance as flbers, both animal and vegetable, starch and gluten. paraflin, various organic materials, etc. In general, my invention is applicable and gives improved results wherever froth flotation flnds application; and may also be utilized where only aeration with air or other gas is desired, for example in the oxidation of various sulphate to ferric salts in solution by aeration.

Throughout this specification and in the claims, the term "circuit has been used in its broad sense, to mean any fluid entity to which aeration or the froth-flotation process is being applied.

I claim as my invention:

1. An agitation-froth flotation apparatus, comprising a cell having agitation and froth-settling chambers, the agitation chamber being oblong in horizontal cross-section, and a verticalaxis rotatable impeller disposed in said agitation chamber nearer one end than the other, said two chambers communicating with each other through an opening near that end of the agitation chamber remote from said impeller.

2. An agitation-froth flotation apparatus, comprising a cell having agitation and froth-settling chambers, the agitation chamber being oblong in horizontal cross-section and a vertical-axis rotatable impeller disposed in said agitation chamber nearer one end than the other, said two chambers communicating with each other through an opening near that end of the agitation chamber remote from said impeller, said opening extending vertically for approximately the full efl'ective height of said chambers.

3. An agitation-froth flotation unit, comprising a cell having interconnected agitation and settling chambers, a vertical-axis impeller displaced horizontally a material distance from the center of said agitation chamber, and means for supplying-a gas to said agitation chamber at a point near the bottom thereof.

4. In a process of separating ingredients of a pulp by froth flotation, the step of swirling a body of the pulp to create a vortex therein while shearing the pulp on curved lines eccentric to the axis of the vortex, said curved lines on which the pulp is sheared being of different elevation, the curvature of the shearing-paths near the bottom of the body of the pulp being of greater raudius than those near the top of the body oi D D- MAHLIN S. HANSEN. 

